1. Field Of The Invention
The present invention generally relates to improvements in the die plate of an underwater pelletizer. More specifically, the invention relates to a tapered insert die plate providing a surface-to-surface contact between the insert and die plate to facilitate removal of and insertion of the insert and substantially improve heat transfer from the outside ring of the die plate to the die insert. The tapered insert is retained in place by hold down bolts which serve as jack bolts to force the insert out of the outer ring of the die plate by insertion into screw threaded holes in the insert to abuttingly engage a flange surface on the outer ring of the die plate to facilitate extraction of the insert when required. The die plate insert includes a plurality of orifices extending therethrough through which molten polymers are extruded in a conventional manner with the tapered surface-to-surface contact between the insert and the die plate providing improved heat transfer from the outside ring of the die plate to the die plate insert as compared with other known techniques of mounting an insert in a die plate.
2. Description Of The Prior Art
Prior U.S. Pat. No. 4,621,996 issued Nov. 11, 1986 discloses an extrusion die plate having a removable central insert provided with extrusion orifices therein in which the insert is screw threadedly mounted in the outer ring of the die plate. This type of structure operates satisfactorily but in some instances, it is difficult to remove the insert from the outer ring of the die plate when it is desired to replace the insert. The prior art of record in that case and the following U.S. patents are also relevant to developments in this field of endeavor.
U.S. Pat. No. 4,269,584 PA1 U.S. Pat. No. 4,710,113 PA1 U.S. Pat. No. 4,764,100 PA1 U.S. Pat. No. 4,934,916 PA1 U.S. Pat. No. 3,323,170 PA1 U.S. Pat. No. 3,355,767
None of the prior art discloses an arrangement in which an underwater plastic pelletizer includes an extrusion die plate having a central insert provided with extrusion orifices which is provided with a tapered external surface for surface-to-surface engagement with a correspondingly tapered internal surface on the outer ring of the die plate. Further, the prior art does not disclose an arrangement in which the hold down bolts which retain the insert in place in the outer ring of the die plate are removed and used as jack bolts to extract the central insert from the outer ring of the die plate.